Outdoor uses of radio communications are many, such as hiking, camping, hunting, biking, warehousing, construction, security, etc. One example of a communication device for these applications is a portable two-way FM transceiver that utilizes an earphone-microphone to transmit via vibrations in the auditory canal. This system provides rudimentary communications, but suffers from poor intelligibility of the spoken word. In these applications, communications involves the use of a microphone that is exposed to winds. Microphones used outdoors are subject to background noise. One method typically used to reduce environmental noise in microphone assemblies is the well-known noise canceling microphone. They are sometimes also referred to as pressure gradient microphones. These microphones consist of a vibratable diaphragm which is actuated by speech or other sounds. The diaphragm is arranged so that sound paths are provided through ports to both the front and rear sides thereof. Far field signals, consisting of environmental noise, reach both sides of the diaphragm simultaneously and are canceled. Near field signals, such as the user's voice, predominately reach only one side of the diaphragm, and are not canceled. Prior art microphones of this type are unsuitable for use in high wind environments because they are ineffective due to the directional nature of wind. Optimal sound characteristics and reproduction of natural sound for a communication device also requires a flat frequency response to a near field sound source. In a noise canceling microphone, the frequency response varies with the acoustic loading on the two ports.
Wind noise is caused by the wind vibrating the diaphragm of the microphone, creating a signal which can be equal to or greater than the user's voice signal, thereby obliterating the voice message. One method of reducing wind noise is to cover the microphone with a layer of foam. The foam ball wind suppresser, typically used by television reporters, is a well-known example of this type of wind noise reducing mechanism. Unfortunately, these types of suppressers are only effective in light winds. In strong winds, such as those experienced by a rider on a bicycle or motorcycle, for example, the foam suppresser does not adequately remove the background wind noise, and the voice signal is unintelligible.
A third source of noise in microphones used outdoors is vibrational noise. This noise arises from mechanical vibrations transmitted to the microphone diaphragm through the mounting structure and the housing. Sources of mechanical vibrations in vehicle mounted microphones are road vibration, engine vibrations, noise from a moving bicycle chain, and other mechanical noise induced by the vehicle.
None of the conventional microphone designs are suitable for use in an environment that has high winds and vibrations. Furthermore, noise canceling microphones are not noted for their environmental sealing ability, and are thus unsuitable for use in inclement weather.